The present invention relates to a steering gear for turning steerable wheels of a vehicle upon rotation of a steering wheel. More specifically, the present invention relates to a steering gear having an electric assist motor.
Known steering gears include a steering member which is axially movable to effect turning movement of steerable vehicle wheels. An electric assist motor drives a mechanism, such as a ball nut which is drivingly connected to a thread portion of the steering member. The electric assist motor drives the ball nut in response to a torque applied to a steering wheel. As the electric assist motor drives the ball nut, the steering member moves axially in response to rotation of the ball nut to turn the vehicle wheels.
There is a relatively small amount of friction in a steering system having an electric assist motor. During a power failure, power to the electric assist motor is cut off. When the steering wheel is released by a vehicle operator after a steering maneuver and when power to the electric assist motor is cut off, the steering member may move past a straight ahead position due to the lack of friction in the steering gear. The steering member may then move to the other side of the straight ahead position and may continue to oscillate back and forth on opposite sides of the straight ahead position.